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Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2024). Probing the CP nature of the top–Higgs Yukawa coupling in tt¯H and tH events with H→bb¯ decays using the ATLAS detector at the LHC. Physics Letters B, 849, Article ID 138469.
Open this publication in new window or tab >>Probing the CP nature of the top–Higgs Yukawa coupling in tt¯H and tH events with H→bb¯ decays using the ATLAS detector at the LHC
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2024 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 849, article id 138469Article in journal (Refereed) Published
Abstract [en]

The CP properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb−1 of proton–proton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of s=13 TeV. The CP structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of b-quarks and produced in association with either a pair of top quarks, tt¯H, or a single top quark, tH. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in tt¯H and tH events, where dedicated CP-sensitive observables are exploited. In an extension of the Standard Model (SM) with a CP-odd admixture in the top–Higgs Yukawa coupling, the mixing angle between CP-even and CP-odd couplings is measured to be α=11−73∘∘+52∘, compatible with the SM prediction corresponding to α=0.

Place, publisher, year, edition, pages
Elsevier B.V., 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344008 (URN)10.1016/j.physletb.2024.138469 (DOI)001185312700001 ()2-s2.0-85185283920 (Scopus ID)
Note

QC 20240229

Available from: 2024-02-28 Created: 2024-02-28 Last updated: 2024-05-03Bibliographically approved
Jackson, P., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., Shaheen, R., . . . et al., . (2024). Search for high-mass resonances in final states with a Formula Presented-lepton and missing transverse momentum with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 109(11), Article ID 112008.
Open this publication in new window or tab >>Search for high-mass resonances in final states with a Formula Presented-lepton and missing transverse momentum with the ATLAS detector
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2024 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 109, no 11, article id 112008Article in journal (Refereed) Published
Abstract [en]

A search for high-mass resonances decaying into a Formula Presented-lepton and a neutrino using proton-proton collisions at a center-of-mass energy of Formula Presented is presented. The full run 2 data sample corresponding to an integrated luminosity of Formula Presented recorded by the ATLAS experiment in the years 2015-2018 is analyzed. The Formula Presented-lepton is reconstructed in its hadronic decay modes and the total transverse momentum carried out by neutrinos is inferred from the reconstructed missing transverse momentum. The search for new physics is performed on the transverse mass between the Formula Presented-lepton and the missing transverse momentum. No excess of events above the Standard Model expectation is observed and upper exclusion limits are set on the Formula Presented production cross section. Heavy Formula Presented vector bosons with masses up to 5.0 TeV are excluded at 95% confidence level, assuming that they have the same couplings as the Standard Model Formula Presented boson. For nonuniversal couplings, Formula Presented bosons are excluded for masses less than 3.5-5.0 TeV, depending on the model parameters. In addition, model-independent limits on the visible cross section times branching ratio are determined as a function of the lower threshold on the transverse mass of the Formula Presented-lepton and missing transverse momentum.

Place, publisher, year, edition, pages
American Physical Society (APS), 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-348755 (URN)10.1103/PhysRevD.109.112008 (DOI)2-s2.0-85196090421 (Scopus ID)
Note

QC 20240628

Available from: 2024-06-27 Created: 2024-06-27 Last updated: 2024-06-28Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2024). Search for New Phenomena in Two-Body Invariant Mass Distributions Using Unsupervised Machine Learning for Anomaly Detection at √s = 13 TeV with the ATLAS Detector. Physical Review Letters, 132(8), Article ID 081801.
Open this publication in new window or tab >>Search for New Phenomena in Two-Body Invariant Mass Distributions Using Unsupervised Machine Learning for Anomaly Detection at √s = 13 TeV with the ATLAS Detector
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2024 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 132, no 8, article id 081801Article in journal (Refereed) Published
Abstract [en]

Searches for new resonances are performed using an unsupervised anomaly-detection technique. Events with at least one electron or muon are selected from 140 fb−1 of pp collisions at √s ¼ 13 TeV recorded by ATLAS at the Large Hadron Collider. The approach involves training an autoencoder on data, and subsequently defining anomalous regions based on the reconstruction loss of the decoder. Studies focus on nine invariant mass spectra that contain pairs of objects consisting of one light jet or b jet and either one lepton (e; μ), photon, or second light jet or b jet in the anomalous regions. No significant deviations from the background hypotheses are observed. Limits on contributions from generic Gaussian signals with various widths of the resonance mass are obtained for nine invariant masses in the anomalous regions.

Place, publisher, year, edition, pages
American Physical Society (APS), 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344327 (URN)10.1103/PhysRevLett.132.081801 (DOI)001190886300010 ()38457710 (PubMedID)2-s2.0-85186742137 (Scopus ID)
Note

QC 20240314

Available from: 2024-03-13 Created: 2024-03-13 Last updated: 2024-05-02Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2024). Search for quantum black hole production in lepton + jet final states using proton-proton collisions at vs = 13 TeV with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 109(3), Article ID 032010.
Open this publication in new window or tab >>Search for quantum black hole production in lepton + jet final states using proton-proton collisions at vs = 13 TeV with the ATLAS detector
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2024 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 109, no 3, article id 032010Article in journal (Refereed) Published
Abstract [en]

A search for quantum black holes in electron + jet and muon + jet invariant mass spectra is performed with 140 fb-1 of data collected by the ATLAS detector in proton-proton collisions at √s = 13 TeV at the Large Hadron Collider. The observed invariant mass spectrum of lepton + jet pairs is consistent with Standard Model expectations. Upper limits are set at 95% confidence level on the production cross section times branching fractions for quantum black holes decaying into a lepton and a quark in a search region with invariant mass above 2.0 TeV. The resulting quantum black hole lower mass threshold limit is 9.2 TeV in the Arkani-Hamed-Dimopoulos-Dvali model, and 6.8 TeV in the Randall-Sundrum model.

Place, publisher, year, edition, pages
American Physical Society, 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344604 (URN)10.1103/PhysRevD.109.032010 (DOI)001183228500014 ()2-s2.0-85187155078 (Scopus ID)
Note

QC 20240321

Available from: 2024-03-20 Created: 2024-03-20 Last updated: 2024-04-03Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2024). Study of High-Transverse-Momentum Higgs Boson Production in Association with a Vector Boson in the qqbb Final State with the ATLAS Detector. Physical Review Letters, 132(13), Article ID 131802.
Open this publication in new window or tab >>Study of High-Transverse-Momentum Higgs Boson Production in Association with a Vector Boson in the qqbb Final State with the ATLAS Detector
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2024 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 132, no 13, article id 131802Article in journal (Refereed) Published
Abstract [en]

This Letter presents the first study of Higgs boson production in association with a vector boson (V ¼ W or Z) in the fully hadronic qqbb final state using data recorded by the ATLAS detector at the LHC in proton-proton collisions at √s = 13 TeV and corresponding to an integrated luminosity of 137 fb−1. The vector bosons and Higgs bosons are each reconstructed as large-radius jets and tagged using jet substructure techniques. Dedicated tagging algorithms exploiting b-tagging properties are used to identify jets consistent with Higgs bosons decaying into bb̄. Dominant backgrounds from multijet production are determined directly from the data, and a likelihood fit to the jet mass distribution of Higgs boson candidates is used to extract the number of signal events. The VH production cross section is measured inclusively and differentially in several ranges of Higgs boson transverse momentum: 250–450, 450–650, and greater than 650 GeV. The inclusive signal yield relative to the standard model expectation is observed to be μ = 1.4+1.0−0.9 and the corresponding cross section is 3.1 ± 1.3(stat)+1.8−1.4(syst) pb.

Place, publisher, year, edition, pages
American Physical Society (APS), 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-345741 (URN)10.1103/PhysRevLett.132.131802 (DOI)001202030300001 ()38613283 (PubMedID)2-s2.0-85189480721 (Scopus ID)
Note

QC 20240418

Available from: 2024-04-18 Created: 2024-04-18 Last updated: 2024-05-24Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . Zwalinski, L. (2024). Study of Z → llγ decays at √s=8 TeV with the ATLAS detector. European Physical Journal C, 84(2), Article ID 195.
Open this publication in new window or tab >>Study of Z → llγ decays at √s=8 TeV with the ATLAS detector
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2024 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 84, no 2, article id 195Article in journal (Refereed) Published
Abstract [en]

This paper presents a study of Z -> ll gamma decays with the ATLAS detector at the Large Hadron Collider. The analysis uses a proton-proton data sample corresponding to an integrated luminosity of 20.2 fb(-1) collected at a centre-of-mass energy root s = 8 TeV. Integrated fiducial cross-sections together with normalised differential fiducial cross-sections, sensitive to the kinematics of final-state QED radiation, are obtained. The results are found to be in agreement with state-of-the-art predictions for final-state QED radiation. First measurements of Z -> ll gamma gamma decays are also reported.

Place, publisher, year, edition, pages
Springer Nature, 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-346061 (URN)10.1140/epjc/s10052-024-12471-9 (DOI)001185550100001 ()2-s2.0-85195377511 (Scopus ID)
Note

QC 20240502

Available from: 2024-05-02 Created: 2024-05-02 Last updated: 2024-06-27Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . Zwalinski, L. (2023). A search for heavy Higgs bosons decaying into vector bosons in same-sign two-lepton final states in pp collisions at √s = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP) (7), Article ID 200.
Open this publication in new window or tab >>A search for heavy Higgs bosons decaying into vector bosons in same-sign two-lepton final states in pp collisions at √s = 13 TeV with the ATLAS detector
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2023 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, article id 200Article in journal (Refereed) Published
Abstract [en]

A search for heavy Higgs bosons produced in association with a vector boson and decaying into a pair of vector bosons is performed in final states with two leptons (electrons or muons) of the same electric charge, missing transverse momentum and jets. A data sample of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb(-1). The observed data are in agreement with Standard Model background expectations. The results are interpreted using higher-dimensional operators in an effective field theory. Upper limits on the production cross-section are calculated at 95% confidence level as a function of the heavy Higgs boson's mass and coupling strengths to vector bosons. Limits are set in the Higgs boson mass range from 300 to 1500 GeV, and depend on the assumed couplings. The highest excluded mass for a heavy Higgs boson with the coupling combinations explored is 900 GeV. Limits on coupling strengths are also provided.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
Higgs Physics, Hadron-Hadron Scattering, Proton-Proton Scattering
National Category
Subatomic Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-338903 (URN)10.1007/JHEP07(2023)200 (DOI)001061852200001 ()
Note

QC 20231031

Available from: 2023-10-31 Created: 2023-10-31 Last updated: 2023-10-31Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2023). A search for new resonances in multiple final states with a high transverse momentum Z boson in √s = 13 TeV pp collisions with the ATLAS detector. Journal of High Energy Physics (JHEP), 2023(6), Article ID 36.
Open this publication in new window or tab >>A search for new resonances in multiple final states with a high transverse momentum Z boson in √s = 13 TeV pp collisions with the ATLAS detector
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2023 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2023, no 6, article id 36Article in journal (Refereed) Published
Abstract [en]

A generic search for resonances is performed with events containing a Z boson with transverse momentum greater than 100 GeV, decaying into e + e − or μ + μ −. The analysed data collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider correspond to an integrated luminosity of 139 fb −1. Two invariant mass distributions are examined for a localised excess relative to the expected Standard Model background in six independent event categories (and their inclusive sum) to increase the sensitivity. No significant excess is observed. Exclusion limits at 95% confidence level are derived for two cases: a model-independent interpretation of Gaussian-shaped resonances with the mass width between 3% and 10% of the resonance mass, and a specific heavy vector triplet model with the decay mode W′ → ZW → ℓℓqq. [Figure not available: see fulltext.]

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
Beyond Standard Model, Hadron-Hadron Scattering, Particle and Resonance Production
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-331636 (URN)10.1007/JHEP06(2023)036 (DOI)2-s2.0-85161946420 (Scopus ID)
Note

QC 20230714

Available from: 2023-07-14 Created: 2023-07-14 Last updated: 2023-08-29Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2023). Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle X in hadronic final states using √s=13  TeV pp collisions with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 108(5), Article ID 052009.
Open this publication in new window or tab >>Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle X in hadronic final states using √s=13  TeV pp collisions with the ATLAS detector
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2023 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 108, no 5, article id 052009Article in journal (Refereed) Published
Abstract [en]

A search is presented for a heavy resonance Y decaying into a Standard Model Higgs boson H and a new particle X in a fully hadronic final state. The full Large Hadron Collider run 2 dataset of proton-proton collisions at √s=13  TeV collected by the ATLAS detector from 2015 to 2018 is used and corresponds to an integrated luminosity of 139  fb−1. The search targets the high Y-mass region, where the H and X have a significant Lorentz boost in the laboratory frame. A novel application of anomaly detection is used to define a general signal region, where events are selected solely because of their incompatibility with a learned background-only model. It is constructed using a jet-level tagger for signal-model-independent selection of the boosted X particle, representing the first application of fully unsupervised machine learning to an ATLAS analysis. Two additional signal regions are implemented to target a benchmark X decay into two quarks, covering topologies where the X is reconstructed as either a single large-radius jet or two small-radius jets. The analysis selects Higgs boson decays into b¯b, and a dedicated neural-network-based tagger provides sensitivity to the boosted heavy-flavor topology. No significant excess of data over the expected background is observed, and the results are presented as upper limits on the production cross section σ(pp→Y→XH→q¯qb¯b) for signals with mY between 1.5 and 6 TeV and mX between 65 and 3000 GeV.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2023
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-340744 (URN)10.1103/PhysRevD.108.052009 (DOI)001088448300001 ()2-s2.0-85175428199 (Scopus ID)
Note

QC 20231212

Available from: 2023-12-12 Created: 2023-12-12 Last updated: 2023-12-12Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2023). ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset. European Physical Journal C, 83(7), Article ID 681.
Open this publication in new window or tab >>ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset
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2023 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 83, no 7, article id 681Article in journal (Refereed) Published
Abstract [en]

The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of s=13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model tt¯ events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.

Place, publisher, year, edition, pages
Institute for Ionics, 2023
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-334799 (URN)10.1140/epjc/s10052-023-11699-1 (DOI)001062397400001 ()2-s2.0-85167625195 (Scopus ID)
Note

QC 20230901

Available from: 2023-09-01 Created: 2023-09-01 Last updated: 2023-10-17Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-5935-7464

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